Heat exchanger element



p 1965 T. F. PAULS HEAT EXCHANGER ELEMENT 2 Sheets-Sheet 1 Filed Dec.29, 1955 mum me 77mm) E #4146 a ,97ToR/ty Sept. 21, 1965 T. F. PAULSHEAT EXCHANGER ELEMENT 2 Sheets-Sheet 2 FIGS.

Filed Dec. 29, 1955 FIG,9.

FIGJI,

HI 5mm HHHH FIG-JO,

M F O'V gw.

United States Patent 3,206,838 HEAT EXCHANGER ELEMENT Theron F. Pauls,Godfrey, Ill., assignor to Olin Mathieson Chemical Corporation, EastAlton, 11]., a corporation of Virginia Filed Dec. 29, 1955, Ser. No.556,225 3 Claims. (Cl. 29157.3)

This invention relates to a heat transfer device and more particularlyto a heat exchanger tube having integral fins.

It is desirable that heat exchange tubing for boilers, refrigerators,condensers and the like be provided with external fins. Such heattransfer fins are usually brazed or soldered on the tubing except wherethe tube structure is very heavy and permits the fins to be cast,extruded, or rolled. However, especially where the tubing is of the fiator oblong sheet metal type, thin walled tubing and the fins are usuallybrazed or soldered together. This is not only expensive and timeconsuming, but frequently fails to result in a rigid and efiicientjoint. Generally, a brazed or soldered joint is of reduced heat exchangeefficiency for lack of unimpeded heat transfer through the joint.Another heretofore known method of forming fins is a helical rollingmethod which, however, has the disadvantage of requiring a fully formedround tube blank together with an internal mandrel and which has thefurther disadvantage of requiring a considerably thick tube wall andcomplicated apparatus and controls for the proper extension of integralfins. This prior method is not readily adapted to formation of fins inconjunction with relatively thin sheet metal walls.

One object of this invention, therefore, is to provide a simple, lowcost but improved design of finned heat exchanger tube. Another objectis to provide a thin walled, relatively flat, sheet metal tube having aplurality of integral fins on the external surface of the tube forimproved heat transfer eificiency. Another object is to provide animproved method of making a tubular form of heat exchanger unit havingan extended heat transfer surface. Still another object is to provide amethod adapted to high speed mass production of finned tubing from sheetmetal.

Other objects and advantages will be evident from the followingdescription of a preferred embodiment of this invention when taken inconnection with the accompanying drawing in which:

FIG. 1 is a plan elevational view of a typical portion of one embodimentof the tubing;

FIG. 2 is a cross sectional view taken on line 11-11 of FIGURE 1;

FIG. 3 is a perspective view of the tubing of FIGURE 1 with portionsbroken away and shown in section on line III-III of FIGURE 1;

FIG. 4 is a cross-sectional view of another embodiment shown between theplatens of apparatus used in its manufacture;

FIG. 5 is a semi-diagrammatic, elevational view showing the process ofmanufacturing tubing in accordance with this invention;

FIG. 6 is a plan view taken on line VI-VI of FIG- URE 5 showing aportion of the apparatus and material in the process of FIGURE 5;

FIG. 7 is a fragmentary view in cross section showing a flat uninflatedtube sheet between grooved die platens suitable for manufacturing theembodiment of FIGURES 1, 2, and 3;

FIG. 8 is a fragmentary view in cross section showing a flat uninflatedtube strip in a die arrangement suitable for manufacturing theembodiment of FIGURE 4;

FIG. 9 is a partial elevational view showing a portion Patented Sept.21, 1965 of a radiator core including the finned sheets of thisinvention;

FIG. 10 is a fragmentary view showing another form of heat exchangerusing the element of thi invention; and

FIG. 11 is a semi-diagrammatic representation of portions of swagingrolls capable of forming the finned strip of the elements shown inFIGURE 10.

The foregoing objects are achieved in accordance with this invention byproviding a novel method of forming a new type of finned tubingcharacterized by a relatively thin walled structure compared to theextension of the fins. The present invention is especially adaptable tomanufacture of integrally finned tubing from a fiat, collapsed butinflatable tube blank. It is contemplated, according to this invention,that the exterior surfaces of an elongated, double walled, sheet metalblank be provided with transversely and longitudinally extending finstogether with intervening wall portions of extreme thinness supportedadequately by the fins. An elongated tube blank is provided havingdouble walls, the opposed interior surfaces of which are contiguous butseparable except at peripheral portions such as the lateral edges whichare joined or welded together in any suitable manner but preferably bypressure or roll welding and this blank is then subjected to deformationto simultaneously thin the opposed tube walls and elevate the fins fromthe material of the walls. Adherence preventing conditions aremaintained during the deformation operation while the fins are beingforged or swaged from the sheet material of the walls which arepreferably of sheet metal. It is also preferred that adherencepreventing material be maintained at the interface between the opposedwalls during the fin forming operation.

Except for the longitudinally extending fins at the lateral edges of thetube blank, the fins formed are preferably transverse and of greatestoutward extension between and remote from the lateral edges of theelongated sheet unit and of least extension adjacent one or both of thelateral edges. This fin shape is of advantage both during and aftererection of walls of the finished tubing.

At this stage, the tube blank characterized by extreme thinness betweenfin extension, is adapted to generation of a tubing passageway by fluidinflation especially where the fins are tapered down at the lateraledges. Following inflation there is produced a new type of sheet metaltubing of extreme wall thinness together with considerable finextension. Although the tube blank may be opened or inflated to anysuitable cross sectional shape, it is preferably formed by inflation torelatively flat or oblong shape. The tubing, when of fiat or oblongshape, preferably has a series of transverse fins extending be tween theopposed lateral edges forming longitudinally extending fins or ribs.Thus, it is contemplated that seamless, relatively flat or oblong tubesbe provided with integral transverse ribs or fins by swaging or forgingWhile in the collapsed or uninflated condition after which the tube wallis erected to provide an internal fluid passageway.

It is further contemplated that the finned tubing be formed in such away that the lateral edges are pressure roll welded togethersimultaneously with the forging or sw'aging of the fins. This can beaccomplished with suitable rolls so that while the fins are being formedthe lateral edge portions are being integrated. This may be efiFected bya reduction of sufiicient severity in thickness of superimposed sheets,pressure welding temperatures between rolls such as 97 and 98, suitablyadapted for this purpose, to pressure weld desired portion of thecomponent sheets while forming the desired fins at spaced points on theexternal faces of the component sheet.

I The fins are integral with the tube walls.

The special finned tube of the illustrative specific embodiment shown inFIGURES l, 2 and 3 consists of first side wall 1, the opposite side wall2, both of which are integrated or preferably joined together bypressure welding at the lateral edges 3 and 4 so as to form at theselateral edges a unitary structure completely sealed together andrequiring no extraneous brazing or welding materials. Side wall 1 bearsa series of external fins 5, while side wall 2 bears correspondingexternal fins 6. It is to be noted that in the medial section of sidewalls 1 and 2, these side walls are extremely thin between the fins 5and 6, respectively. This makes for more efficient and improved heattransfer through the side walls and to the fins. At the lateral edges 3and 4, the thickness of the structure is considerably greater than thatof the side walls. This makes for improved longitudinal rigidity andruggedness of structure.

Pins 5 and 6 are of greater extension at a point intermediate theirends. It is to be noted, for example, that -fin 5 is of greaterextension at the midpoint 7 than at its ends 11 and 9. Likewise, eachfin 6 on the other side is of greater extension at midpoint 8 than atthe end portions 10 and 12. This construction provides not only improvedheat exchange but also needed rigidity at the thinnest portions of thewalls 1 and 2 and enables them to better resist distention under highinternal pressure. Thus desirable increase in fin extension is producedtogether with a desirable thinness of intervening tube wall. The two inconjunction make for most efficient heat transfer. The single fluidpassageway 13, generated by bulging of the walls 1 and 2 in any suitableWay but preferably by inflation, is of lenticular shape in general. Theshape of this passageway, however, can vary from the extremes of anovoid shape to a rather flat oblong or nearly rectangular shape.

The fins of the embodiment of FIGURES l, 2 and 3 can be formed withapparatus as shown in FIGURE 7 where is the working end of an upperforging die and -16 is the working end of a lower forging die.

These operate upon special flat, laminated stock 200 having the opposedcomponent layers 201 and 202 joined at their lateral edges at 19 and butmaintained in separation at 12 between these lateral edges in anysuitable manner while in contiguity. For example, at 12 there may beprovided a thin layer of any suitable weld or adherence preventingmaterial.

Die block 15 is provided with a series of grooves between protrudinglands 17. In similar manner, die block 16 has a grooved working faceprovided with a series of spaced lands 18 in registry with the lands 17of block 15. Each of the lands or teeth 17 and 18 are shaped in thisembodiment by tapering lengthwise to be of greatest protrusion, which isto say closest approach, adjacent their midsections with respect to thecorresponding opposing land. This die face arrangement works thegreatest deformation of component sheets 201 and 202 adjacent thelongitudinal midplane of the special completely annealed blank 200 andprovides the greatest extension of the fins 5 and 6 (FIGURE 3). Theseare produced as an integral part of the tube as the forging dies 15 and16 are brought into engagement with the blank 200 with desired pressureor impact. The resulting uneven deformation of the blank produces theintegral fins 5 and 6 tapered down at ends 9 and 11 and 10 and 12 asshown in FIGURES 1, 2 and 3. Lateral edges 13 and 20 of the blank 200are either left of original thickness or increased somewhatin thickness.Inasmuch as the greatest deformation is produced uniformly along thelongitudinal midsection of the blank, the metal at this section is giventhe greatest work hardening effect while the metal adjacent the lateraledges is relatively soft and adapted for permitting inflation of theblank between any suitable known sizing dies or platens or forpermitting bulging with a suitable mandrel. When the blank, now not onlyinternally laminated but also externally finned, is of very long length,it is preferably bulged by injection of inflation fluid pressure betweensizing platens to give desired longitudinal uniformity of erection ofthe walls 1 and 2 and generation of the internal passageway 13.

The embodiment of the tube structure of this invention shown .in FIGURE4 is characterized by a streamlined or tear drop cross sectionalconfiguration. In this embodiment, the finished tube consists of sidewall 31, which bears a series of external fins 35, and the opposing sidewall 32, which bears a similar series of external fins 36. These finsare of greatest outward extension adjacent the leading lateral edge 34of this embodiment of the tube. Thus, the leading edge 37 of fins 35 andthe leading edge 38 of fins 36 protrude considerably to form a generousrounded streamlined leading fin section. Adjacent the trailing lateraledge 33 of the .tube, the fins 35 and 36 are tapered down to mergegradually into the opposing side walls 31 and 32, which as in theprevious embodiment are integrated at both the edges 34 and 33.

This embodiment of FIGURE 4 can advantageously be formed from thespecial blank 300 in the apparatus shown in FIGURE 8, after which thestructure is infiated to the final finished form shown in FIGURE 4between the spaced sizing platens 39 and 40 (FIGURE 4) the working facesof which are closely spaced adjacent the trailing end 33 and moreremotely spaced adjacent the leading edge 34. First of all, however,special fiat blank 308, preferably in completely annealed condition, isplaced in the die cavity of the block 50 (FIGURE 8) where it issupported upon the grooved working face of the lower movable forging ram56, also nested in the cavity of the block 50. Upper forging ram or die55 is movable into the cavity of block 50 and is adapted together withlower ram 56 to subject blank 300 to forging or swaging action. It is tobe noted that in the apparatus of FIGURE 8, as contrasted with theapparatus of FIG- URE 7 the lateral edges of the blank are confined,thus edge 333, which will form trailing edge 33 of the finished tube,and also edge 334 of the blank 300, which will form the leading edge 34of the tube are confined in the cavity of the die block 50. The workingfaces of the forging rams 55 and 56 are provided with a series of spacedteeth or lands 57 and 58, respectively. These, it will be noted, arelocated only adjacent edge 334 and the adjoining portion of the internallamination or interface of separation 312. But adjacent the other edge333 of the blank, forging lands 57 and 58 are tapered back so as toaccomplish less finning and resultant forging of the blank 300. Thinningand forging in this embodiment is accomplished all the way to the outerperiphery of the lateral edge 334. It will be understood, that withsuitable symmetry in the blank 300, the forging lands 57 and 58 mayextend uniformly all the way across the working face of the forging rams55 and 56, respectively, to proivde fins substantially completely acrossthe tube structure as, for example, shown in FIGURE 10.

Upon completion of the forging operation, blank 300 now provided with aseries of external fins on both sides, is then placed between suitablyseparated platens 39 and 40 (FIGURE 4) and subjected to internalinflation pressure so as to produce the shape of the finished tube shownin FIGURE 4 having the fluid passageway 43.

In any event, and for the production of the foregoing or any otherembodiments, there is provided a fiat twowalled blank in any suitablemanner. Such a blank may formed by rolling or drawing a relativelythin-walled tube shut. Also the blank may be formed by extrusion afterwhich the extruded blank may be flattened either by rolling or passagethrough a sizing or drawing die. If naturally occurring oxide within theinterior of such a blank is insufficient for the purpose, an adherencepreventing coating may be applied to the interior of the blank so as toprevent undesired sticking between the opposing walls of the blankduring the rolling, drawing or the subsequent forging operationdescribed herein. However, a preferred mode of providing the blank is tobring two strips of relatively thin material into superposition with anintervening layer of weld or adherence preventing material between thecomponent sheets except at the lateral edges and then subjecting thesuperposed assembly to sufiicient deformation to accomplish pressurewelding of the lateral edges of the assembly. This blank is thensuitable and ready for swaging or forging to form the desired finnedtube structure.

An illustrative example of a process for making a finned tube blank inaccordance with this invention is shown in FIGURES 5 and 6. The finnedblank 79 produced is ready for erection to the final finished hollowform. As shown in FIGURE 5, long, relatively narrow component strips 61and 62 are paid off from coils 63 and 64, respectively, of any suitablematerial such as aluminum, copper, steel, their alloys and the like. Thefaces of strips 61 and 62 which are to be juxtaposed are in someinstances subjected to scratch brushing by the rotary brushes 65 and 66,respectively; and to the scratch brushed surface of one of the strips,namely 61, there is applied parallel spaced stripes 75 (FIGURE 6) ofweld-preventing material by means of a grooved applicator roll 67operating from its slurry 68 of weld-preventing material. The adherent,thin layer of material 75 is then dried by any suitable means, such asthe heater coil 69, after which the component strips 61 and 62 arebrought into contiguity at the pinch rolls 70 just prior to entry of theassembly into the heating furnace 71, where the assembly is heated to adesired pressure welding temperature. The assembly of component stripsand weld-preventing stripes 75 issuing from the furnace is then passedbetween the welding rolls of the mill 72. This accomplishes a pressureweld between component strips 61 and 62 at the intervening areas betweenthe Weld-preventing stripes 75. Next, specially welded and laminatedsheet 74 issuing from the mill 72 is cut up into individual tube strips76 by passage between slitter rolls 73. Each of the tube strips 76 isthen subjected to a swaging or forging operation between the groovedwork faces of die blocks 77 and 78 so as to provide the integrallyfinned tube sheet blank 79.

The individual finned tube strips produced may then be erected to thehollow form in any suitable manner. Injection of internal fluid pressureinto the stratum of parting may be employed; or a suitable tool such asa shaped and pointed mandrel may be forced down the lamination of eachstrip, particularly when in relatively short lengths, to accomplishopening of the internal fluid passageway.

The individual finned tubes may be assembled together as shown in FIGURE9 to make a radiator core. In this instance each tube 80 is providedwith a series of opposing fins 85 and 86 on the opposite faces as in theprevious embodiments. However, each tube 80 is also provided with aspecial construction at each end to adapt the tubes to be assembled withthe orificed header plates 87 and 88 of the core. At each end there isprovided an outwardly extending flange or hilt 89 against which eitherplates 87 and 88 may be seated. The end structure of the tubes 80 islikewise characterized by an end portion 81 free from any fins so as topermit the ends of the tubes 80 to be passed through suitable openingsin the header or end plates 87 and 88.

In FIGURE there is shown a strap type of heat exchanger 90 made inaccordance with this invention. The unit is provided with a single heatexchanger fluid passageway 113, one end of which at 91 is constricted soas to enable inlet connection to be made with ordinary tubing 111. Atthe other end 92 the unit is similarly constructed for connection withoutlet tube 112. Between these ends there are provided on the exteriorof unit 90 a series of transverse integral fins such as 95 extending allthe way across the unit 90 including the lateral edges 93 and 94.

To produce the external fins in this embodiment, there 6 may be providedthe swaging rolls 97 and 98 of FIGURE 11 instead of the reciprocatingforging dies described hereinbefore. Rolls 97 and 98, the latter ofwhich is flanged on both ends, have a peripheral construction suitablefor manfacturing the fin structure and strip of FIG- URE 10. It will beunderstood that the roll periphery may have grooved or toothed formsidentical or similar to the working faces shown in FIGURES 7 and 8. Eachroll is provided with protruding forging teeth or lands,

such as teeth of roll 97 and teeth 106 of flanged roll 98. These teethare designed to come into registry in opposition to each other at theroll bite at which the roll spacing is adapted to accomplish the desiredswaging and flow of metal needed to make the fins. The roll 97 and theroll 98 is each free from the forging teeth over a portion of theirperipheries such as 103 and 104, respectively, so that these recessedportions of the periphery may leave the ends 91 and 92 of the unit ofFIGURE 10 free from fins. At this recessed portion of the rolls 97 and98 there is provided a pair of registerable pinch off sharp protrusionssuch as 101 and 102, respectively. When these come together intosubstantial contact and registry, desired measured portions of the stripare cut apart from each other.

Among the advantages of the construction of this tubing is that not onlyare the tube walls desirably thinned and provided with heat transferelements for more eflicient heat conduction but also that the walls ofthe tubing itself are stiflFened by the cold formed ribbing thusincreasing the safety factor of the tubing and its resistance againstundesired deflection under high internal pressure. The lateral edgeshave the effect, especially when the relatively massive cross section ofa longitudinal stiffening and shape holding member. This adapts thetubes for being formed to various substantially self-retaining heatexchanger core tube configurations. The metal of the tube in the finsand adjacent the fins is most severely worked and, therefore, admirablysuited to necessitate undesired deflection of the tube walls. The crosssectional shape of the tube, which in general is lenticular or oblongand relatively flat, is advantageous for many heat exchanger structures.

While embodiments of this invention now believed to be preferred aredisclosed herein, it is to be understood that other embodiments, changesand modifications may occur to those skilled in the art withoutdeparting from the spirit and scope of this invention as set forth inthe appended claims.

What is claimed is:

1. The method of making seamless, finned tubing comprising providing asuperposed pair of component sheets having weld-preventing materialbetween them except at laterally spaced portions, reducing the thicknessof the superposed assembly of said sheets at spaced intervals moreseverely than between said spaced intervals thereby simultaneouslywelding said sheets at said laterally spaced portions and formingexternal fins intermediate said intervals and intermediate saidlaterally spaced portions, and thereafter separating said sheetsintermediate said lateral portions to final tube form having at leastone longitudinally extending passageway in the tubing.

2. The continuous method of making seamless, finned heat exchangertubing comprising superposing in substantial contiguity a pair ofcontinuous component sheet metal strips together with an interposed thinlayer of weld-preventing material between the juxtaposed weldablesurfaces of said strip except adjacent the lateral edge portions of thestrips, progressively reducing the thickness of said superposed stripsand interposed material with concomitant longitudinal elongationsufliciently at a suitable temperature to accomplish integration of saidcomponent strips at said lateral edge portions, progressively swagingsaid integrated strips at least intermediate said lateral edge portionssutficiently to form external, transversely extending, longitudinallyspaced fins integral with said sheet metal strips and thereafterinjecting inflation fluid pressure between said component strips alongsaid weld-preventing material to distend said strips and finally formfinished tubing having a fluid passageway in the tubing.

3. The method of forming a finned heat exchanger of the roll bonded typewhich comprises, superimposing flat metal sheets having stop-Weldmaterial located therebetween, said stop-weld material being arranged ina predetermined internal passage configuration, forge-welding saidsheets together by hot-rolling except for the passage configurationdefined by said stop-weld material, simultaneously forming die extrudedprotuberances on each of the outer surfaces of said sheets bycompressing said sheets between a pair of die members, and subsequentlyapplying fluid pressure to the area of said sheets defined by saidstop-Weld material to move apart the non-bonded por tions of saidsheets.

References Cited by the Examiner UNITED STATES PATENTS 8 1,951,394 3/34Chase 29157.3 2,154,216 4/39 Savage 257256 2,549,446 4/51 Hoheisel29157.3 2,626,130 1/53 Raskin 257-256 5 2,662,273 12/53 Long 29157.32,690,002 9/54 Grenell 29157.3 2,722,048 11/55 Gier 29l57.3 2,765,52610/56 Sparkes et a1. 10 2,906,006 9/59 Neel 29-1573 FOREIGN PATENTS2,008,626 7/35 Belgium.

110,363 5/00 Germany. 15 4,794 2/ 94 Great Britain. 619,672 3/49 GreatBritain. 736,705 9/55 Great Britain.

87,268 4/56 Norway.

Examiners.

1. THE METHOD OF MAKING SEAMLESS, FINNED TUBING COMPRISING PROVIDING ASUPERPOSED PAIR OF COMPONENT SHEETS HAVING WELD-PREVENTING MATERIALBETWEEN THEM EXCEPT AT LATERALLY SPACED PORTIONS, REDUCING THE THICKNESSOF THE SUPERPOSED ASSEMBLY OF SAID SHEETS AT SPACED INTERVALS MORESEVERELY THAN BETWEEN SAID SPACED INTERVALS THEREBY SIMULTANEOUSLYWELDING SAID SHEETS AT SAID LATERALLY SPACED PORTIONS AND FORMINGEXTERNAL FINS INTERMEDIATE SAID INTERVALS AND INTERMEDIATE SAIDLATERALLY SPACED PORTIONS, AND THEREAFTER SEPARATING SAID SHEETSINTERMEDIATE SAID LATERL PORTIONS TO FINAL TUBE FORM HAVING AT LEAST ONELONGITUDINALLY EXTENDING PASSAGEWAY IN THE TUBING.